Preparing aromatic mercaptans



, ThisL invention relates Patentedl July 29, 1952 2,605,289 -PREPARING ARoMA'rro MERCAPTANS' i George H. Daniels and John VerbancQWilmington, Del., assignors to E. 1. du Pontdey Nemours & Company, Wilmington, Del., acorporation of Delaware A iNoDrawing. Application February 9,-150, v

` i Serial N-1435356 to ar method for preparing methyl substituted aromatic mercaptans,` particularlyA from their corresponding polysuldes .The `rnostcommon method, which has been employed in the past for preparing aromatic mercaptans, comprises reacting an aromatic hydrocarbon with chlorosulfonic acid to form an aryl sulfonyl chloride and reducing the aryl sulfonyl chlorideby-treatment with zinc dust and an aqueous acid, such asa-hydrochloric acid.' lThe aromatic mercaptans, produced byl such process, are expensive, due primarily to the large amount of zinc dust required.

More recently, a method has been developed for making aryl mercaptans at a substantially lower cost than by the above chlorosulfonicacid process.l Such'latter method comprises condensing an aromatic hydrocarbonwith sulfur monochloride to produceya mixture of aromatic sulfides -composedfprimarily of aromaticfpolysuldes as described by Signaigo in Patent 2,402,685, then reducing suchcrude mixture, preferably, with an alkali sulde in aqueous causticv solution, andy then acidifying the reduced mixture to liberate the free mercaptan. Such mixturefof'aromatic polysulj fides can also be reduced` tothe corresponding mercaptansby; catalyticA hydrogenation or by treatmentwith agents, 'jsuch "as zinc. dust and" an l aqueous acid', Vhydrogen sulfide, an alkali amalgam, metallic sodium, etc.

It is an -object'of our invention vto' provide a method for preparing methyl substituted" phenyl mercaptans at lower cost than the methods previcusly employed or suggested. Another lobject is '-to provide a novel method for' preparing methyl substituted phenyl mercaptans from thecorresponding cli-(methyl substituted phenyl) polysuldes. A further object is to. provide a method for preparing methyl substituted phenyl mercaptans in high yields by the pyrolysis of the corresponding di-(methyl substituted phenyl) 'polysuldes. Other objects areto advance the'y art.

Still other objects Will appear herenafter-` 12 claims. (o1. 26o-soa) y' i i understood sen-se tomea-n the monovalent` radical theoretically derived bythe removal of one hydroeen .atom frombenzerle.. The term:methy1 Sublstituted phenylv refers to .azphenylg radical in which from 1 to 5 hydrogenatoms have been replaced .by methyl groups @1 -11st .A di-(methyl substituted phenyl). nolrsulde? iol 'disulde refers to those compounds in which 2 methyl substituted phenyl radicals are joined together by 2 or more sulfur atoms, each methyl substituted phenyl radical being Abonded' directly to a different sulfur atom.

The di-(methyl substituted phenyl) polysulfides, which-are to ide-employed yin'iour method, are 'those-which contain-from l.- to 5 methyl groups, such as ditolyl polysuliides, -dixyl'yl polysuldes, mesitylenepolysuldesfdurene polysuldes, etc. 'Our process is particularly-adapted to the treatment of suclr polysuldes in which each phenyl radical cor-itains only 11) to 2 methyl radij cals, i. e., the ditolyl polysulildes and the diXylyl y polysu-ldes. Also', qurlprocess'is' particularly adaptedto thel treatment of thed-isuldes. The

dij-(methyl substituted phenyl) polysulides may `be single pure compounds, mixturesrof twoor corresponding mercaptan s,1 Particularly valuable sllifces of the'd'i-(methyl more of such poly'sulides; orcrude'reaction mixtures such 'as are obtained inthemanufacture'oi the polysulfides. rIhe di-(m-ethyl substituted phenyl) polysuldes may bemade by any of the known methods, such as the oxidation of the substituted phenyl) p olysulid'es are the-,crude reaction products obtained vby condensing the corresponding aromatic' hydrocarbon wthfsulfur'v monochloride as' described'by Signaigo in vlatent 2,402,685, For example, d'ixylyl polysuldes may b-e'made in this "manner from 3'xylen e,

The `above and other "objects, of our invention may be accomplishedl byheating vat. least one di-(methyl substituted phenybrpolysulfide ata temperature 'of `fronr2005n C. to` 350 Cfunder a pressure below 150mm.v of'mercury absolutaand removing'the mercaptans from'the reaction mass. By such method, the polysulfides are converted to the 'corresponding' methyl'substituted phenyl mercaptans economically and in good yields.

'.Suchprocess is simple and easy to operate and control. '.1 e, n e The term' 'pheny1" is' employed in its commonly 'which is a 4 mix'ture"of ortho, meta andpara Xylenes.V When suchV products are'mad'e, employing a 10 to 1 mol ratio'. of hydrocarbon to sulfur monochloride, the crude solvent-free mixture contains about '70 weight percent of polysuldes reducible to the aromaticl mercaptan by treatment with zinc' dust and acid, the remaining 30 Aweight percent being com-posed primarily of moncsulfides. While it is unnecessary to remove Vthe inert solvents or the by-products ofthe condensation reaction from such crude reaction products, prior to treating them fbyi theprocess of our invention, it will generally be preferred to remove thesolvents beforesotreati-ngthem. j

The temperaturesto beemrlieyed' our. method may range from 200 C. 15oabout 35Q C'. At temperatures below 200 C., little or no conversion As theversion and purity of the products rapidly decreases, the conversions decreasing from at least 40% at pressures below 150 mm. to about 12% at atmospheric pressure. Optimum conversions and purest products are obtained at pressures below 100 mm. of mercury absolute and par..

ticularly at pressures below 50 mm.

While it is not necessary to remove the mercaptans from the reaction mass and reaction zone as rapidly as they are generated,l optimumyields are obtained if the mercaptans are removed from the reaction mixture continuously during the reaction and substantially as rapidly as they are generated. y

In order to more clearly illustrate our invention, suitable modes of carrying the same into eiect and the advantageous results to be obtained thereby, the vfollowing examples are given:

' EXAMPLE 1 Di-para-tolyl disulde was prepared by the oxidation of the sodium salt of para-thiocresol with hydrogen peroxide. About 100 grams of .the diepara-tolyl disulde was placed in a 0.5

liter round-bottomvflask equipped with a 30 xY 1 inch rvacuum-ja,cketed fractionating column packed with glass helices. An appropriate distillation head and receiver surmounted the column. The pressure in. the system was reduced to 1-2' mm. of mercury absolute and the flaskv contents were-heated to 235-250 C. Under these conditions, lsubstantially pure para-thiocresol distilled continuously until the reaction 4 was complete after. about V2l hours. About 44% of the di-p'ara-tolyl disulfide was converted to pure para-thiocresol.

EXAMPLE 2 Mixtures oi dixylyl disulfldes were prepared by the hydrogen peroxide oxidation of the sodium salts of a mixture of isomeric xylyl mercaptans which had beenmadeby the chlorosulfonic acid process from 3 xylene (a, mixture of ortho, meta and para xylenes). Samples of such mixtures were converted to pure xylyl mercaptans by 'treatment in the apparatus of Example 1 at various temperatures and pressures with the results shown in the following Table I:

Table I Reaction Conversion Absolute Y Sample Teglgra' Pressure ngrcg'aln C. Mm' Hg percent EXAMPLE 3 A solvent-free sample of the crude reaction product, obtained by condensing 3 xylene with sulfur monochloride in a to 1 mol ratio, was treated in the apparatus ,of Example 1. This captan.

2,605,289 .s A t sample was a mixture of xylyl sulfides, including some dixylyl monosuli'lde as well as dixylyl disuldes and higher sulfides. The pressure in the system was reduced to 2-5 mm. of mercury absolute and the ask contents were heated to 225-250 C. About 52% of the xylyl polysulfides were convertedto purexylyl-mercaptans.

When this example wasrepeated,'employing a pressure of about 1 mm. of mercury absolute and a temperature slightly below 200 C., the

maximum conversion to mercaptan was only 2%.

EXAMPLE 4 YClaisen flask equipped with an appropriate rel ceiver. -Pressure in the system was reduced to 2 mm. of mercury and the ask contents then were heated to 198 C. to initiate distillation. The temperature of the flask contents was iny creased toa maximum of 226 C. during the 2.5

hours required for, the distillation. The distillateweighed 56 grams andvanalyzed 41 per cent xylyl mercaptan. This represents a conversion to mercaptan of ,40 per cent of the tetrasuli'lde.

1115 grams of the crude solvent-freereaction products, obtained by condensing 3 4xylene with sulfur monochloride ina 10 to 1 mol ratio. was placed in a 2 liter iron pot equipped` with a 16 x l inch vacuum-jacketed fractionating column packed with glass helices. y The column was surmounted by an appropriate distillation head and receiver.U YAbsolute pressure in the system was reduced and maintainedl Ybetween 50 land mm. of mercury. At a pot contents temperature between 220 and 280 vC., xylyl mercaptan distilled continuously during a 4.75 hour reaction period. The distillate weighed 515 grams and analyzed 97.4 per cent xylyl mer- This represents-a conversion to pure mercaptan of 45 per cent of the crude solventfree reaction products.

It will bevunderstood -tlfiatfthe preceding examples are given for illustrative purposes solely and that our. invention is notblimited to the speciiic embodiments disclosed. therein. Other di-(methyl substituted phenyl) "polysuli-ldes may be substituted for those in the examples. The temperatures and pressure may be varied within Vthe broad ranges hereinbefore disclosed.- Also,

other apparatusmay be used and Avarious forms of apparatus will 4be readily` apparent to those skilled in the art. Wh'ile'the, examples show the carrying out of the process in batches, it will be readily apparent thatthe process may be carried out continuouslyrwith,continuous separation and removalv oflthe mercaptans and It will appear that,;byour'nvention. We have yprovided a novel process -for 4preparing methyl absolute, and removing the mercaptans from the reaction mass.

2. The method for making methyl substituted phenyl mercaptans which comprises heating at least one di-(methyl substituted phenyl) polysulfide at a temperature of from 200 C. to about 300 C. under a pressure below 150 mm. of mercury absolute, and removing the mercaptans from the reaction mass.

3. The method for making methyl substituted phenyl mercaptans which comprises heating at least one (li-(methyl substituted phenyl) polysulfide at a temperature of from 200 C. to 350 C. under a pressure below 100 mm.'of mercury absolute, and removing the mercaptans from the reaction mass.

4. The method for making methyl substituted phenyl mercaptans which comprises heating at least one di-(methyl substituted phenyl) polysulde at a temperature of from 200 C. to about 300 C. under a pressure below 100 mm. of mercury absolute, and removing the mercaptans from the reaction mass.

5. The method for making methyl substituted phenyl mercaptans which comprises heating at least one cli-(substituted phenyl) polysulde in which the substituents 0n each phenyl radical consist of 1 to 2 methyl radicals at a temperature of from 200 C. to 350 C. under a pressure below 150 mm. of mercury absolute, and removing the mercaptans from the reaction mass.

6. The method for making methyl substituted phenyl mercaptans which comprises heating at least one di-(substituted phenyl) polysulflde in which the substituents on each phenyl radical consist of 1 to 2 methyl radicals at a temperature of from 200 C. to about 300 C. under a pressure below 100 mm. of mercury absolute, and removing the mercaptans from the reaction mass.

7. The method for making Xylyl mercaptans which comprises heating at least one dixylyl polysulfide at a temperature of from 200 C. to 350 C.

under a pressure below 150 mm. of mercury absolute, and removing the xylyl mercaptans from the reaction mass.

8. The method for making Xylyl mercaptans which comprises heating at least one diXylyl p0lysulde at a temperature of from 200 C. to about 300 C. under a pressure below 100 mm. of mercury absolute, and removing the xylyl mercaptans from the reaction mass.

9. The method for making xylyl mercaptans which comprises heating a mixture of dixylyl polysuldes at a temperature of from 200 C. to 350 C. under a pressure below 150 mm. of mercury absolute, and removing the Xylyl mercaptans from the reaction mass.

l0. The method for making Xylyl mercaptans which comprises heating a mixture of dixylyl polysulfldes at a temperature of from 200 C'. to about 300 C. under a pressure below 100 mm. of mercury absolute, and removing the Xylyl mercaptans from the reaction mass.

11. The method for making a thiocresol which comprises heating a ditolyl disulfide at a temperature of from 200 C. to 350C. under a pressure below 150 mm, of mercury absolute, and removing the thiocresol from the reaction mass.

12. The method for making a thiocresol which comprises heating a ditolyl disulfide at a temperature of from 200 C. to about 300 C. under a pressure below mm. of mercury absolute, and removing the thiocresol from the reaction mass.

GEORGE H. DANIELS. JOHN J. VERBANC.

REFERENCES CITED UNITED STATES PATENTS Name Date Gilbert et al. May 2, 1950 Number 

1. THE METHOD FOR MAKING METHYL SUBSTITUTED PHENYL MERCAPTANS WHICH COMPRISES HEATING AT LEAST ONE DI-(METHYL SUBSTITUTED PHENYL) POLYSULFIDE AT A TEMPERATURE OF FROM 200* C. TO 350* C. UNDER A PRESSURE BELOW 150 MM. OF MERCURY ABSOLUTE, AND REMOVING THE MERCAPTANS FROM THE REACTION MASS. 